Wire bonders are conventionally used during semiconductor assembly and packaging for making electrical wire connections between electrical contact pads on a semiconductor chip and a substrate, or between electrical contact pads on different semiconductor chips. Specifically, a bonding wire is fed from a wire spool containing the bonding wire through a bonding tool, such as a capillary, for performing a wire bonding process. By using a combination of heat, pressure and ultrasonic energy, the bonding wire is bonded or welded to a connection pad of the semiconductor chip or the substrate. The wire bonding process is a solid phase welding process, wherein two metallic materials (i.e. the bonding wire and the connection pad surface) are brought into intimate contact. Once the surfaces are in intimate contact, electron sharing or interdiffusion of atoms takes place, resulting in the formation of a wire bond.
Calibration of wire bonders is required to ensure performance consistency across different wire bonders. At present, the calibration of wire bonders includes the following steps:    1) Using an external laser vibrometer or optical vibrometer to measure ultrasonic vibration of the wire bonder's transducer tip or capillary tip;    2) Recording bonding results such as ball size, ball shear, number of ball lift, bond pad peeling after wire pull, etc.; and    3) Using an external force sensor to calibrate the bond force based on the measured ultrasonic vibration and recorded bonding results.
The above method of calibrating wire bonders has the following shortcomings:
1) As the method takes a long time to measure the bonding results, for example the ball size and ball shear, a user normally derives these measurements based on a limited range of ultrasonic vibration of the wire bonder's transducer tip and this affects the calibration accuracy.
2) As the use of the external laser vibrometer or optical vibrometer involves other equipment for measuring the ultrasonic vibration of a wire bonder's transducer tip, a long setup time may be needed.
3) As the method does not simulate the actual operation of wire bonders, it may not be accurate.
4) As the external force sensor requires additional equipment to calibrate the wire bonder, calibration of wire bonders may take a long time.